Organic light emitting diode display

ABSTRACT

An organic light emitting diode (OLED) display is provided. The OLED display includes: a substrate member; an OLED that includes a pixel electrode that is formed on the substrate member, an organic light emitting layer that is formed on the pixel electrode, and a transflective common electrode that is formed on the organic light emitting layer; an encapsulation thin film that is formed on the transflective common electrode; and a touch panel that includes a first touch conductive layer that is formed on the encapsulation thin film and that is formed with a transflective metal film, a glass substrate that is formed on the first touch conductive layer, and a second touch conductive layer that is formed on the glass substrate. In some embodiments, the transflective common electrode has reflectivity of less than 50%. Some of the external light is thus reflected again to the first touch conductive layer and back to the transflective common electrode and so on. During this cycling, destructive interference occurs and the cycled light eventually dissipates. Thus, unwanted reflected light is suppressed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean PatentApplication No. 10-2008-0083395 filed in the Korean IntellectualProperty Office on Aug. 26, 2008, the entire contents of which areincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an organic light emitting diode (OLED)display. More particularly, the present invention relates to an OLEDdisplay including a touch panel

2. Description of the Related Art

A typical OLED display includes a plurality of organic light emittingdiodes having a hole injection electrode, an organic emission layer, andan electron injection electrode. Light is emitted as excitons aregenerated. The excitons are generated as electrons and holes arecombined and drop from an excited state to a ground state. The OLEDdisplay displays an image by using the light resulting from theseexcitons.

Accordingly, an OLED display has self-luminance characteristics, andunlike a liquid crystal display (LCD), the thickness and a weightthereof can be reduced since a separate light resource is not required.Further, OLED displays are used in various applications, such asdisplays in mobile electronic devices, because an OLED display has lowpower consumption, high luminance, and high reaction speed. Furthermore,OLED displays with a touch panel have become widely used.

However, the hole injection electrode and an electron injectionelectrode in the OLED display and several other metal wires can reflectlight from the outside. This reflection can deteriorate an OLED'sdisplay characteristics, such as black color expression and contrast.

In order to compensate for the reflection of external light, some knownOLED displays employ a polarizing plate and a phase delay plate tosuppress the reflected light. However, in conventional OLEDs, use of apolarizing plate and a phase delay plate can cause a considerable amountof loss of light that is generated in the organic emission layer of theOLED. Furthermore, in conventional OLEDs, use of a polarizing plate anda phase delay plate may make the OLED device overly thick and unsuitablefor use with a touch panel.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

Embodiments of the present invention provide an OLED display havingimproved visibility by suppressing reflection of external light, such asambient light. In addition, embodiments of the present invention canprovide an OLED display having suitable thickness for use with a touchpanel.

An exemplary embodiment of the present invention provides an OLEDdisplay including: a substrate member; an OLED that includes a pixelelectrode that is formed on the substrate member, an organic lightemitting layer that is formed on the pixel electrode, and atransflective common electrode that is formed on the organic lightemitting layer; an encapsulation thin film that is formed on thetransflective common electrode; and a touch panel that includes a firsttouch conductive layer that is formed on the encapsulation thin film andthat is formed with a transflective metal film, a glass substrate thatis formed on the first touch conductive layer, and a second touchconductive layer that is formed on the glass substrate.

The transflective common electrode may have reflectivity of less than50%. The transflective common electrode may be made of a co-depositedmaterial including at least one of magnesium (Mg) and silver (Ag).Furthermore, in the OLED display, the transflective common electrode maybe formed with a metal film of at least one of magnesium (Mg), silver(Ag), calcium (Ca), lithium (Li), and aluminum (Al).

The encapsulation thin film may have an average refractive index of 1.6or more. The encapsulation thin film may have a thickness in a range of400 Å to 1300 Å. The encapsulation thin film may be formed byalternately stacking a plurality of organic films and inorganic films.

The first touch conductive layer may have a thickness in a range of 50 Åto 150 Å. The first touch conductive layer may include any one ofmagnesium (Mg), silver (Ag), calcium (Ca), lithium (Li), chromium (Cr),and aluminum (Al). Surfaces of the encapsulation thin film may closelycontact the transflective common electrode and the first touchconductive layer, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout view of an OLED display according to a firstexemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of the OLED display taken along lineII-II of FIG. 1.

FIG. 3 is an enlarged cross-sectional view of a dotted line circle ofFIG. 2.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The present invention will be described with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. Those skilled in the art will realize that the describedembodiments may be modified in various different ways, all withoutdeparting from the spirit or scope of the present invention. Constituentelements having the same configuration are representatively describedwith reference to one or more embodiments. Other exemplary embodimentsmay then be described by referring to various differences between theembodiments. The drawings and description are to be regarded asillustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

In the drawings, the thickness of layers, films, panels, regions, etc.,may be exaggerated for clarity. In addition, the size and the thicknessof each element in the drawing are provided for better understanding andease of description of various embodiments and are not intended to limitthe present invention. For example, it should be understood that when anelement, such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. When an element is referred toas being “directly on” another element, there are no interveningelements present.

In the accompanying drawings, an organic light emitting diode (OLED)display is illustrated. For purposes of illustration, an active matrix(AM)-type OLED display is shown having a 2Tr-1Cap structure in which twothin film transistors (TFTs) and one capacitor are formed in one pixel.But, the embodiments of the present invention are not limited thereto.Other OLED display embodiments consistent with the present invention canhave various structures. For example, three or more TFTs and two or morecapacitors can be provided in one pixel of an OLED display, and separatewires can be further provided in the OLED display.

One skilled in the art will recognize that the term pixel can refer to aminimum unit for displaying an image. An OLED display displays an imageby using a plurality of pixels, and thus, has a plurality of pixelareas.

An embodiment of the present invention will now be described withreference to FIGS. 1 to 3. As shown in FIG. 1, the OLED display 100 caninclude a switching TFT 10, a driving TFT 20, an organic light emittingdiode (OLED) 70 in one pixel, and a capacitor 80. The OLED display 100further includes a gate line 151 that is disposed along one direction, adata line 171 that is insulated from and intersects the gate line 151,and a common power line 172. In the example shown, the boundary of onepixel may be defined by the gate line 151, the data line 171, and thecommon power line 172. Further, the OLED display 100 further includes anencapsulation thin film 800 (shown in FIG. 2) and a touch panel 90(shown in FIG. 2).

In general, the switching TFT 10 operates by a gate voltage that isapplied to the gate line 151. The switching TFT 10 transfers a datavoltage applied to the data line 171 to the driving TFT 20. Capacitor 80stores a voltage corresponding to a difference between a common voltageapplied from the common power line 172 to the driving TFT 20 and a datavoltage transferred from the switching TFT 10. From the capacitor 80, acurrent flows to the OLED 70 through the driving TFT 20, which causesthe OLED 70 emits light. Some of these components will now be furtherdescribed.

The switching TFT 10 includes a switching semiconductor layer 131, aswitching gate electrode 152, a switching source electrode 173, and aswitching drain electrode 174. The switching TFT 10 is used as a switchfor selecting a pixel to emit light. The switching gate electrode 152 isconnected to the gate line 151. The switching source electrode 173 isconnected to the data line 171. The switching drain electrode 174 isseparated from the switching source electrode 173 and is connected tothe first sustain electrode 158.

The driving TFT 20 applies driving power and enables the organicemission layer 720 of the OLED 70 within the selected pixel to emitlight to the pixel electrode 710. The driving TFT 20 includes a drivingsemiconductor layer 132, a driving gate electrode 155, a driving sourceelectrode 176, and a driving drain electrode 177. The driving gateelectrode 155 is connected to the first sustain electrode 158. Each ofthe driving source electrode 176 and the second sustain electrode 178 isconnected to the common power line 172. The driving drain electrode 177is connected to the pixel electrode 710 of the OLED 70 through a contacthole 182.

The OLED 70 includes a pixel electrode 710, an organic emission layer720 that is formed on the pixel electrode 710, and a transflectivecommon electrode 730 (shown in FIG. 2) that is formed on the organicemission layer 720. Here, the pixel electrode 710 is a positive (+)electrode, which is a hole injection electrode. The transflective commonelectrode 730 is a negative (−) electrode, which is an electroninjection electrode. However, the present invention is not limitedthereto. For example, the pixel electrode 710 may be a cathode, and thetransflective common electrode 730 may be an anode.

Holes and electrons are injected into the organic emission layer 720from the pixel electrode 710 and the transflective common electrode 730,respectively. Excitons are generated when injected holes and electronsare coupled and fall from an excited state to a ground state. Light isthen emitted when the excitons are generated.

The capacitor 80 includes a first sustain electrode 158 and a secondsustain electrode 178 with a gate insulating layer 140 (shown in FIG. 2)disposed therebetween.

A structure of the OLED display 100 will now be described further withreference to FIG. 2. As shown in FIG. 2, an OLED display 100 includesthe driving TFT 20, the OLED 70, and the capacitor 80, and also includesan encapsulation thin film 800 and a touch panel 90. In the embodimentshown, the driving TFT 20 is a TFT having a PMOS structure and using aP-type impurity. However, the present invention is not limited thereto.For example, the TFT 20 can also be an NMOS structure TFT or a CMOSstructure TFT.

Furthermore, the driving TFT 20 that is shown in FIG. 2 is a polycrystalTFT including a polysilicon film. The switching TFT 10 (not shown inFIG. 2) may be a polycrystal TFT or an amorphous TFT having an amorphoussilicon film. Some of the other differences between the switching TFT 10and the driving TFT 20 may also be apparent from the figures.

In the driving TFT 20, the substrate member 110 is formed with aninsulation substrate consisting of glass, quartz, ceramic, plastic, etc.However, the present invention is not limited thereto. For example, thesubstrate member 110 may be formed with a metal substrate like stainlesssteel.

A buffer layer 120 is formed on the substrate member 110. The bufferlayer 120 can prevent penetration of impurities into the substratemember 112 and may provide a planarization surface. The buffer layer 120may be made of various materials that can perform these functions. Forexample, the buffer layer 120 may include any one of a silicon nitride(SiNx) film, a silicon oxide (SiO₂) film, and a silicon oxynitride(SiOxNy) film. The buffer layer 120 is not always necessary, and thus,may be omitted in some embodiments according to the type and processconditions of the substrate member 110 used.

The driving TFT 20 also includes a driving semiconductor layer 132, adriving gate electrode 155, a driving source electrode 176, and adriving drain electrode 177. One skilled in the art will recognize thatthe configuration of the driving TFT 20 is not limited to the describedexamples, but can be variously changed into other configurations.

The driving semiconductor layer 132 is formed on the buffer layer 120.The driving semiconductor layer 132 is formed with a polysilicon film.Further, the driving semiconductor layer 132 includes a channel region135 in which impurities are not doped. The source region 136 and a drainregion 137 may be formed with doping of p+ at both sides of the channelregion 135. The doped ion material can be a P-type impurity, such asboron (B) material like B₂H₆. Different impurities can be employedaccording to the kind of TFT used.

A gate insulating layer 140 that is made of silicon nitride SiNx orsilicon oxide SiO₂ is formed on the driving semiconductor layer 132. Agate wire including the driving gate electrode 155 is formed on the gateinsulating layer 140. The gate wire further includes the gate line 151(shown in FIG. 1), the first sustain electrode 158, and other wires. Thedriving gate electrode 155 is formed to be overlapped with at least apart of the driving semiconductor layer 132, particularly, a channelregion 135.

An interlayer insulating layer 160 for covering the driving gateelectrode 155 is formed on the gate insulating layer 140. The gateinsulating layer 140 and the interlayer insulating layer 160 havethrough-holes for exposing a source region 136 and a drain region 137 ofthe driving semiconductor layer 132. The interlayer insulating layer 160is made of silicon nitride (SiNx) or silicon oxide (SiO₂), etc., as inthe gate insulating layer 140.

A data wire is formed on the interlayer insulating layer 160 andincludes a driving source electrode 176 and a driving drain electrode177. The data wire further includes the data line 171 (shown in FIG. 1),the common power line 172, the second sustain electrode 178, and otherwires. The driving source electrode 176 and the driving drain electrode177 are connected to the source region 136 and the drain region 137,respectively, of the driving semiconductor layer 132 through thethrough-holes.

A planarization layer 180 for covering the data wires 172, 176, 177, and178 is formed on the interlayer insulating layer 160. The planarizationlayer 180 performs a function of removing a step and planarizing inorder to raise light emitting efficiency of the OLED 70 to be formedthereon. Further, the planarization layer 180 has a contact hole 182 forexposing a part of the drain electrode 177.

The planarization layer 180 may be made of at least one of apolyacrylate resin, an epoxy resin, a phenolic resin, a polyamide resin,a polyimide resin, an unsaturated polyester resin, a poly phenylenetherresin, a poly phenylenesulfide resin, and a benzocyclobutene (BCB).

A pixel electrode 710 of the OLED 70 is formed on the planarizationlayer 180. The pixel electrode 710 is connected to the drain electrode177 through the contact hole 182 of the planarization layer 180.

Further, a pixel defined layer 190 having an opening for exposing thepixel electrode 710 is formed on the planarization layer 180. The pixeldefined layer 190 may be made of a polyacrylate resin and a polyimideresin, or a silica-based inorganic material. The pixel electrode 710 isdisposed to correspond to the opening of the pixel defined layer 190.Therefore, a portion in which the pixel defined layer 190 is formed issubstantially equivalent to the remaining portion, except for a portionin which the pixel electrode 710 is formed.

The OLED 70 can be formed from a pixel electrode 710, an organicemission layer 720, and a transflective common electrode 730. Theorganic emission layer 720 is formed on the pixel electrode 710. Thetransflective common electrode 730 is formed on the organic emissionlayer 720.

The organic emission layer 720 is made of a low molecular organicmaterial or a high molecular organic material. The organic emissionlayer 720 may include multiple layers. For example, the organic emissionlayer 720 may include a hole injection layer (HIL), a hole-transportinglayer (HTL), an emission layer, an electron-transporting layer (ETL),and an electron-injection layer (EIL). The HIL is disposed on the pixelelectrode 710, which is an anode. The HTL, the emission layer, the ETL,and the EIL may then be sequentially stacked thereon.

The OLED display 100 may be a front light emission type. Accordingly,the pixel electrode 710 may be made of a reflective conductive materiallike lithium (Li), calcium (Ca), lithium fluoride/calcium (LiF/Ca),lithium fluoride/aluminum (LiF/Al), aluminum (Al), silver (Ag),magnesium (Mg), or gold (Au). However, the pixel electrode 710 mayinclude other types of layers including a transparent conductive layer,a reflective layer, or a transflective material.

In one embodiment, the transflective common electrode 730 has areflectivity of less than 50%. Any material that has a reflectivity ofless than 50% and transflects light can be used as the transflectivecommon electrode 730.

An encapsulation thin film 800 is formed on the transflective commonelectrode 730. The encapsulation thin film 800 serves as a protectionand covers and seals the TFT 20 and the OLED 70 from the outside. Theencapsulation thin film 800 may have an average refractive index equalto or greater than 1.6 and a thickness t1 in a range of 400 Å to 1300 Å.Further, as shown in FIG. 3, the encapsulation thin film 800 can includea plurality of organic films 820 and inorganic films 810 that arealternately stacked.

Reference will now be made to FIG. 3, which is an enlargedcross-sectional view of a dotted line circle of FIG. 2. As shown in FIG.3, the organic film 820 may be made of polymer and the inorganic filmmay be made of aluminum oxide (Al₂O₃). Through such a configuration, theencapsulation thin film 800 can stably cover the OLED 70 while having arelatively thin thickness t1.

On the encapsulation thin film 800, a first touch conductive layer 930,a touch glass substrate 910, and a second touch conductive layer 920 aresequentially formed. Here, the first touch conductive layer 930, thetouch glass substrate 910, and the second touch conductive layer 920form a touch panel 90.

In some embodiments, the touch panel 90 uses a capacitance method. Thetouch panel 90 is formed by coating a transparent special conductivemetal on both surfaces of the touch glass substrate 910 and forming thefirst touch conductive layer 930 and the second touch conductive layer920. If a voltage is applied to four corners of the touch panel 90, ahigh frequency is spread on a surface of the touch panel 90. When thetouch panel 90 is touched, a controller analyzes the changed highfrequency waveform and recognizes the location of the touch point.

The first touch conductive layer 930 includes any one of magnesium (Mg),silver (Ag), calcium (Ca), lithium (Li), chromium (Cr) and aluminum(Al). Further, the first touch conductive layer 930 can have a thicknesst2 of a range of 50 Å to 150 Å.

In such a configuration, both surfaces of the encapsulation thin film800 are in relatively close proximity to the transflective commonelectrode 730 and the first touch conductive layer 930, respectively.This proximity of the interface may be close enough such that air doesnot substantially exist between the encapsulation thin film 800, thetransflective common electrode 730, and the first touch conductive layer930. Accordingly, the transflective common electrode 730, theencapsulation thin film 800, and the first touch conductive layer 930can also be useful in suppressing the reflection of external light.

The manner in which these components can suppress the reflection ofexternal light will now be further described. First, when external lightpasses through the touch panel 90, some of this light is reflected fromthe first touch conductive layer 930 back to the outside of the device.However, some of the light may advance toward the transflective commonelectrode 730 via the encapsulation thin film 800.

As described above, because the transflective common electrode 730 hasreflectivity of less than 50%, some of the injected light is reflectedagain to the first touch conductive layer 930. Some of light is emittedback to the outside after passing through the first touch conductivelayer 930. The remaining portion is reflected again and advances towardthe transflective common electrode 730. Therefore, this causes a cyclingof light from the outside using the reflection between the transflectivecommon electrode 730 and the first touch conductive layer 930 with theencapsulation thin film 800 interposed therebetween.

During this cycling, destructive interference occurs and the lighteventually dissipates. Therefore, in some embodiments, the encapsulationthin film 800 has a refractive index of greater than or equal to 1.6 andhas a thickness t1 of a range of 400 Å to 1300 Å. However, destructiveinterference of light may occur with other configurations.

Equation 1 may be useful in explaining the principle of destructiveinterference of the reflected light employed in the embodiments. Inparticular, Equation 1 may be expressed as:

d=λ/4Ndcos θ

where “d” is a distance between two reflection surfaces, i.e. athickness of an encapsulation thin film;

“N” is a refractive index of an encapsulation thin film;

“θ” is an incidence angle of light; and

“λ” is a wavelength of reflected light.

For example, assuming a wavelength of green visible light and anincidence angle of 30° to 45°, the application of Equation 1 indicatesthat an encapsulation thin film thickness t1 in a range of 400 Å to 1500Å may be an effective thickness for promoting destructive interferenceof light.

Further, the thickness t2 of the first touch conductive layer 930 is setto effectively transflect light. For example, by closely disposing thetransflective common electrode 730, the encapsulation thin film 800, andthe first touch conductive layer 930, the reflection of external lightcan be substantially suppressed. Thus, the OLED display 100 can haveimproved visibility.

Further, the encapsulation thin film 800 may be formed with a relativelythin thickness t1 and may avoid use of a polarizing plate and a phasedelay plate, which are conventionally used for suppressing reflection ofexternal light. Therefore, since it can omit these components, the OLEDdisplay 100 may have a reduced thickness even though it includes thetouch panel 90.

In some embodiments, the transflective common electrode 730 is made of aco-deposited material including at least one of magnesium (Mg) andsilver (Ag). These materials may be used in order to increase thesuppression of reflected external light.

In yet other embodiments, the transflective common electrode 730 isformed with a metal film of at least one of magnesium (Mg), silver (Ag),calcium (Ca), lithium (Li), and aluminum (Al). That is, thetransflective common electrode 730 may be formed with one metal film andmay be formed with a structure having a stack of a plurality of metalfilms. This configuration may be used in order to increase thesuppression of reflected external light.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An organic light emitting diode (OLED) display comprising: asubstrate member; an OLED that comprises a pixel electrode that isformed on the substrate member, an organic light emitting layer that isformed on the pixel electrode, and a transflective common electrode thatis formed on the organic light emitting layer; an encapsulation thinfilm that is formed on the transflective common electrode; and a touchpanel that comprises a first touch conductive layer that is formed onthe encapsulation thin film and that is formed with a transflectivemetal film, a glass substrate that is formed on the first touchconductive layer, and a second touch conductive layer that is formed onthe glass substrate.
 2. The OLED display of claim 1, wherein thetransflective common electrode has reflectivity of less than 50%.
 3. TheOLED display of claim 2, wherein the encapsulation thin film has anaverage refractive index of 1.6 or more.
 4. The OLED display of claim 3,wherein the encapsulation thin film has a thickness in a range of 400 Åto 1300 Å.
 5. The OLED display of claim 4, wherein the encapsulationthin film is formed by alternative stacking of a plurality of organicfilms and inorganic films.
 6. The OLED display of claim 4, wherein thefirst touch conductive layer has a thickness in a range of 50 Å to 150Å.
 7. The OLED display of claim 6, wherein the first touch conductivelayer comprises any one of magnesium (Mg), silver (Ag), calcium (Ca),lithium (Li), chromium (Cr), and aluminum (Al).
 8. The OLED display ofclaim 1, wherein both surfaces of the encapsulation thin film closelycontact the transflective common electrode and the first touchconductive layer, respectively.
 9. The OLED display of claim 1, whereinthe touch panel is formed in a capacitance method.
 10. The OLED displayof claim 2, wherein the transflective common electrode is made of aco-deposited material comprising at least one of magnesium (Mg) andsilver (Ag).
 11. The OLED display of claim 2, wherein the transflectivecommon electrode is formed with a metal film of at least one ofmagnesium (Mg), silver (Ag), calcium (Ca), lithium (Li), and aluminum(Al).